Biomolecule interactions on calcium carbonate and stoichiometrically similar biomedical, optical and electronic materials

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Abstract

A combinatorial approach has been successfully used to characterize
peptides that bind to four different surfaces of CaCO3 and six different oxide
substrates that are chemically and stoichiometrically similar to CaCO3. A standard
screening and a single substrate screening method were employed. Both methods
used a bacteriophage combinatorial library with a complexity of 109
different
random sequences. While geological (104) calcite screenings do not seem to show
strong consensus, peptides screened against geological aragonite exhibit
extraordinary consensus. Overall, peptides screened against aragonite were highly
basic. Peptides screened against (110) geological aragonite show
[LAIVG]P[WF][RKH] and triple [RKH] patterns. The most significant binding
peptide, A21 (LPPWKHKTSGVA) was found in 4 separate screenings. The (110)
geological aragonite sequences are highly enriched in prolines. Coincidently,
peptides screened against the optical material LiNbO3 +Z show patterns similar to
those found in the aragonite screenings. Other substrates that did not exhibit
strong consensus include powdered LiNbO3, powdered BaTiO3, powdered
PbTiO3, single crystal LiNbO3 –Z, and hydroxyapatite. A database and analysis
program was written to catalog and evaluate the statistical significance of the
many sequences. One peptide that was determined to be extremely significant in
binding to aragonite, A20 (LPKWQERQMLSA), was modeled using umbrella
sampling molecular dynamics techniques as well as analyzed by NMR. It was
determined that there is a good probability that the peptide’s conformation is
helical, but it is able to introconvert between α-helical, 3-10 helical and extended
conformations fast enough that a stable secondary structure is not detectable by
NMR. Engineered phage were constructed to display these significant peptides on
the pVIII surface, increasing the expression level and the long range order in the
hopes of building an aragonite nucleation surface. Hybrid organic-inorganic
materials were grown on the phage resulting in a mixture of the three forms of
CaCO3: calcite, vaterite, and aragonite. In addition, hybrid materials were grown
on the optical waveguide material LiNbO3. Doubly engineered phage were shown
to bind preferentially to the LiNbO3 +Z surface through the interaction of the A1
displayed peptide as well as nucleate semiconducting ZnS particles via the A7
peptide selected previously against ZnS.